The present invention relates to wind turbines for operation at variable speed under varying wind conditions, and, more particularly, to a combination wind turbine and AC power generator coupled to a radially oriented gear train.
Wind turbines provide a method for extracting energy from wind and converting the energy into electricity to be supplied either for individual use or into utility power grids. The conversion of wind energy to electrical energy is accomplished by coupling a turbine through appropriate drive means to an electric power generator so that wind blowing onto the turbine will cause the rotor of the power generator to rotate. Typically, the power generator is an alternating current (AC) induction generator. The generator has stationary field windings which are coaxially wound about a rotor that can be driven by the turbine on the wind turbine. If the electrical power generated by the wind turbine is to be supplied to a utility power grid, then it must have a constant frequency, such as 60 Hz, that is synchronized to the utility line frequency. Some wind turbines accomplish this function by operating at a constant speed. However, more efficient wind turbines operate at variable speed, causing the rotor of the AC generator to rotate at variable speed, resulting in an AC power frequency that is variable. In such variable speed wind turbines, the AC power output of the AC generator is rectified and then applied to an inverter which converts the resultant DC power to AC power at a controlled frequency.
In conventional wind turbines, the components of the power train connecting the turbine or turbine rotor blades to the AC generator rotor are laid out in a straight line. The result is an elongated turbine system which tends to require excessive space, be relatively costly, inefficient in power conversion and sometimes unstable under various forms of dynamic loads from varying wind conditions. Such turbines also may pose difficulty in maintenance due to the requirement for alignment of the axially laid-out elements of the turbine system. More particularly, when the major power train components such as the blade hub rotor, clutch, gear box, brake system and cooling system are laid out in a straight line, as is typical in the prior art, the design is elongated and can be susceptible to rotor dynamic unbalanced loading.